DIY Pagination with DataMapper

There are many pagination solutions out there. Of course there’s the venerable will_pagination and the much newer Kaminari. However, all of the pagination solutions usually contain boiler-plate HTML. What if we only want the pagination logic, maybe in a JSON API, without using Rails or ActiveRecord, but instead Sinatra and DataMapper. As it turns out, DataMapper makes DIY pagination as simple as:

@posts = Post[((page - 1) * per_page), per_page]

As a Sinatra helper method this would look like:

def paginate(query)
  @page     = (params[:page] || 1).to_i
  @per_page = (params[:per_page] || 10).to_i

  query[((@page - 1) * @per_page), @per_page]
end

Now, what if we want to know the total number of pages and records? Enter the dm-chunked_query gem, which provides convenience methods for querying chunks of records:

require 'dm-chunked_query'

def paginate(query)
  @page        = (params[:page] || 1).to_i
  @per_page    = (params[:per_page] || 10).to_i

  @pages       = query.chunks_of(per_page)
  @total_count = @pages.count
  @page_count  = @pages.length

  @pages[@page - 1]
end

Pagination is that simple.